This invention relates to multi-gate switches, and more particularly, to multi-gate electro-mechanical switches that can be configured to store desired switch states.
Integrated circuits often include switches. A switch may be turned on to form an electrical connection across the switch or may be turned off to break the electrical connection. Switches are typically formed from transistors such as metal-oxide-semiconductor (MOS) transistors. The use of electro-mechanical switches such as micro-electro-mechanical (MEM) switches has also been proposed. These switches, which are sometimes referred to as nano-electro-mechanical (NEM) switches, may be formed using microfabrication operations that leverage semiconductor processing techniques such as photolithographic patterning techniques.
A conventional electro-mechanical switch is formed on a substrate. The conventional electro-mechanical switch has a source terminal, a drain terminal, and a gate formed on the substrate. A cantilever beam is formed over the gate. The beam is attached to the source terminal. In its off state, the gate of the switch is driven to a low voltage. The beam has a tip that extends over the drain terminal. In the off state of the switch, the tip and the drain terminal are separated by air. No electrical connection is therefore formed between the source and drain terminals in the off state (e.g., the switch is open).
The gate of the conventional switch can be driven to a high voltage to place the switch in an on state. The source terminal is driven to a low voltage in the on state. In the on state, a gate-to-source voltage (e.g., the voltage difference between the gate and the source terminal) generates an electrostatic force that bends the beam so that the tip of the beam contacts the drain terminal. The beam serves as a conductive path for electrons, thereby forming an electrical connection between the source and drain terminals (e.g., the switch is closed).
Conventional electro-mechanical switches generally have a single gate. As a result, a dedicated controlling circuit (i.e., an address transistor) is required. The controlling circuit is connected to the gate of the switch. The controlling circuit determines whether the switch is turned on or off. For example, the controlling circuit can drive the gate to a high or low voltage to place the switch in an on or off state, respectively.
In a scenario in which more than one switch is used, each switch requires a corresponding controlling circuit to place the switch in its desired state. For example, a 64 by 128 array of switches would require 8192 (64 multiplied by 128) controlling circuits. Thus, in applications that use a large number of single-gate switches, a large number of controlling circuits would also be required to control each switch. The controlling circuits may consume an unacceptably large area on an integrated circuit.
It would therefore be desirable to be able to provide improved electro-mechanical switch circuitry.